This application relates generally to elongated, flexible members that are used to lift and/or suspend and move heavy and/or bulky objects. More particularly, this application relates to lift slings. Even more particularly, this application relates to an apparatus and method of evaluating the physical condition of a lift sling.
In many industries, large and/or heavy objects must be moved from one position to another position, or be lifted to a different elevation, or be loaded onto another object. For objects that are too large, bulky or heavy to be lifted by hand, machines such as cranes or hoists are commonly used. Such machines are usually provided with a cable that is connected to a sheave block or a hook. Often, the sheave block or hook cannot be connected directly to the object to be lifted and instead requires an additional member that is interposed between the sheave block or hook and the object. The additional member is known as a sling. The sling can take different forms, depending upon the nature of the object to be lifted. With the simplest form, the sling comprises an elongated, flexible member or leg, which includes an upper end that is connectable to the sheave block or hook, and a lower end having a fitting that is connectable to the object. Usually, the upper end is connected to an enlarged, closed link, known as a “master link”, but it can also terminate with a fitting such as a hook. With more elaborate forms, which are useful in lifting irregularly shaped, bulky objects, the sling can include two, three, four, or even more elongated, flexible members or legs.
Because slings are often used in harsh, industrial conditions they can be inadvertently or unintentionally damaged. Even a sling used with the utmost of care can, over time, become nicked, cracked, stretched, bent, corroded, or otherwise altered from its original state. These conditions can be the result of overloading, improper storage, interaction with sharp corners, dragging along a floor or an abrasive surface, kinking or twisting, shock loading, hostile environments such as excessive heat or cold, chemicals, weld spatter, etc.
Because of the consequences of using defective slings can be catastrophic, the government, through the occupational safety and health administration (OSHA), has mandated that slings be inspected. Specifically, slings must be inspected before each and every time they are to be used. In addition, slings must be inspected at a minimum of at least once a year. One component of the inspection consists of a visual inspection, with attention being paid to any obvious changes in the slings that are indicative of damage. For example, stretching, bending, nicks, cracks, corrosion. In each instance where one of the above conditions is detected, the sling must be removed from service. However, there are situations in which a sling may be defective, though not visibly so. For, example, a sling may be imperceptibly deformed due to overloading. In such situations, the sling will look normal, but it should be removed from service. Therefore, in addition to visual inspections, a sling must be inspected using changes physical parameters such as link diameter and reach, which also indicate wear and tear.
This application provides an apparatus and method for evaluating elongated lifting members by detecting changes in physical parameters of the lifting members.